In controlling various oil tool equipment, such as blowout preventers, production trees and other hydraulically actuated equipment, it is customary to supply a hydraulic fluid supply at a high pressure, for example, 3,000 psi. However, the equipment works at a pressure lower than the supply pressure and it is necessary to reduce and regulate the pressure to the desired working pressure for the equipment. However, in a pilot controlled pressure reducing and regulating valve if the control system fails, causing a loss of the pilot signal, this is equivalent to venting off the regulated pressure to zero. This means that the equipment being operated by the outlet supply pressure becomes inoperative and in the case of safety equipment, such as oil well blowout preventers, this could lead to disaster. U.S. Pat. No. 4,444,216 and United States patent application Ser. No. 591,369, filed Mar. 20, 1984 now U.S. Pat. No. 4,565,349, entitled "Fail Safe Hydraulic Pilot Pressure Reducing and Regulating Valve", disclosed two types of fail safe systems for use with a pressure reducing and regulating valve.
The present invention is directed to an improved fail-safe system for use on any type of fluid piloted pressure actuated mechanism such as a hydraulically piloted pressure reducing and regulating valve in which the parts are suitable for repair in the field, the fail-safe system can be unlocked with a minimum of pressure and will not be detrimentally affected by higher pressures, and the locking member does not require fluid seals and therefore has no seal drag to affect its sensitivity of adjustment.